This study is a multi-center open-label single dose, dose-escalation cohort protocol to evaluate the safety and preliminary biological efficacy of a gene transfer of the cystic fibrosis gene using recombinant adeno-associated virus vector (a small, non-disease causing virus which has been emptied of its own DNA and packed instead with the DNA for the gene which is defective in cystic fibrosis) delivered to the lower respiratory tract of patients with cystic fibrosis by jet nebulization (mist). Evidence of gene transfer has been sought by measurements of wild-type CF gene DNA in brushed bronchial epithelial cells (airway cells obtained through a scope inserted into the lungs) by a laboratory test called direct PCR, and expression of wild-type CF messenger RNA (meaning the gene is working) in these cells by another, similar test called RT-PCR. In addition, other potential biological measurements of potential efficacy include levels of inflammatory mediators (disease-causing chemicals) in bronchoalveolar lavage fluid (fluid from the lung).